Manufacture of activated carbon



Jan. 26, 1954 J. w. DONEGAN MANUFACTURE OF ACTIVATED CARBON Filed Feb. 28, 1951 Q\ mar quzuommmq A I IINVENTOR. JOSEPH -w. DONEGAN l mwfimmioq \\i ON IKE 3123K i m b i F n v w h /m 55 #2:! W 33m 233: m m m 8 52:65 W mime m w S ATT RNEY.

Patented Jan. 26, 1954 ITED STATE ATENT OFFICE MANUFACTURE OF ACTIVATED CARBON Application February 28, 1951, Serial No. 213,164

8 Claims.

This invention relates to the manufacture of activated carbons from tars and pitches and more particularly refers to a new and improved method of converting the tars and pitches into high yields of activatable char.

In the distillation of crude tars to produce desirable carbolic and creosote oil distillates, a problem of disposing of the resultant pitch residues often exists. The utilization of such residues as fuels represents a substantial depreciation in value of the bituminous products with consequent effective increase in cost for production of the distillates. As described in my copending application Serial No. 18,712, filed April 2, 1948, now Patent 2,549,298, issued April 17, 1951, I have developed a method of separating solid carbonaceous materials susceptible to activation from tars and pitches by the addition of solvent thereto and by subsequent processing to convert the solid carbonaceous materials into activated carbon which has a greatly enhanced value compared to the tar or pitch from which it was derived. The yield of solid carbonaceous materials removed from the tars and pitches for activation ranges from about 10 to 40% by weight dependent upon the nature of the particular tar or pitch employed.

An object of the present invention is to provide a method for converting coal tar pitches, watergas tar pitches and oil-gas tar pitches into high yields of activated carbon with a reduced amount of by-products.

Another object of the invention is to produce increased yields of solid carbonaceous materials from coal tar pitches, water-gas tar pitches and oil-gas tar pitches without the use of solvents.

Other objects and advantages of the present invention Will be apparent from the following description and accompanying drawing.

In general, the present invention involves blowing air through a molten body, i. e. liquid phase, of residual hydrocarbon material boiling above 670 F. until the benzol-in'soluble content of the hydrocarbon material is increased to at least 55% by weight, pulverizing the air-blown hydrocarbon material to at least 80% passing a No. 200 sieve, and calcining the pulverized hydrocarbon material until an infusible activatable char is obtained and then activating the char by steam or flue gases. The pulverule'n't activated char thus obtained is particularly suitable for decolorizing purposes. If it is desired to produce granular activated char suitable as a vapor adsorbent, the pulverized air-blown hydrocarbon material is compressed to form briquettes which are then crushed and sized to the desired size granules and. the latter calcined and activated to activated char.

More specifically, increased yields of activatable char may be obtained from coal tar, watergas tar and oil-gas tar by separating from the tars a high boiling hydrocarbon material substantially free from oils boiling below 670 F. and having a melting point (cube method) within the range of 150 F. to 325 F., preferably between 160 to 250 F., heating the high boiling hydrocarbon to maintain it in a molten condition, passing air or other oxygemcontaining gas in contact with said molten hydrocarbon material maintained-in an agitated state at a temperature between 550 and 950 preferably 650 tau-850 F. for a sufficient length of time to increase the benzol-insoluble content of the hydrocarbon material to in excess of desirably below 90% and preferably between to pulverizing the air-blown hydrocarbon material to preferably below 200 mesh, compressing the pulverized hydrocarbons at pressures preferably ranging from 5000 to- 50,000 p. s. i. to form briquettes, crushing and sizing the briquettes into granules of, e. g., 10 to 20 mesh size, calcining the granules in the presence of oxygencontaining gas at temperatures sufiiciently high to char the granules, preferably at increasing temperatures from below about 400 F. to within the range of 400-850 F., desirably avoidingtemperatures in excess of 750 while maintaining the temperature sufiiciently low during such calcination so that the granules remain in an unfused condition, continuing the calcination until an in'fusible activatable char is obtained, and activating the char at an elevated temperature, generally from 1450 to 2200 F., by the action of steam or due gases.

Tars are conventionally subjected to fractional distillation to separate them into cuts of different boiling points. A typical coke-oven tar will yield on distillation the following:

Per cent (by volume) Carbolic oil 16 Creosote' oil 25 Heavy oil 15 Fuel pitch 41 Loss 3 The carbolic oil and'creosote oil are in demand and bring a high market price. The heavy oil is unsalable as creosote, and is frequently disposed of as fuel, with accompanying loss of value. Likewise, fuel pitch, for the most part has the relatively low value of fuel. I have found that in the practice of my process the undesirable heavy oil can be converted into superior grades of activated carbon and further a greater yield of activated carbon from fuel pitch can be produced than hitherto had been obtained.

The charging stock subjected to treatment in my process may be coal-tar pitch or water-gas tar pitch or oil-gas tar pitch or mixtures of these pitches; such pitches containing substantially no oils boiling below 670 F. and having a, melting point (cube method) between 150 F. and 325 F., preferably 160 to 250 F. The charging stock may be obtained conveniently by distillation, for example, of a typical coke-oven tar into the following cuts:

Per cent (by volume) Carbolic oil 16 Creosote oil 25 Pitch 56 Loss 3 In this distillation only two distillate fractions are obtained, the heavy oil and fuel pitch fractions of the preceding example together comprising the residual pitch. This residual pitch is emlnently suitable for conversion into activated carbon.

The accompanying drawing is a diagrammatic flow .diagram illustrating the process of the present invention.

Referring to the drawing, the charging stock which may be a coal-tar pitch, water-gas pitch or oil-gas pitch derived from the corresponding tars is introduced from storage container 1 through opening 2 into the top of blow still 3. Due to expansion of the charg upon heating and blowing of air therethrough, it is advisable not to fill blow still 3 to a level higher than about of its height. As illustrated in the drawing, the blow still, generally designated by numeral 3, consists of a vertical cylindrical chamber 4 equipped with a power driven agitator 5 of the paddle type. Air or other oxygen-containing gas may be introduced into the top of vertical hollow shaft 6 of agitator 5 and discharged into the body of pitch in blow still 4 through a perforated cross pipe I at the terminal end of shaft 5 near the bottom chamber 4. Gases and vapors are released from the top of still 3 through opening 8. Heat may be applied to the contents of vessel 4 by generating combustion gas in a conventional furnace 9 and passing th hot combustion gas through the annular space bounded by th walls of chamber 4 and jacket H and thence discharging the spent combustion gas through stack !2.

In operation the pitch in blow still 3 is heated to a molten condition, i. e. a liquid phase state, by the transfer of heat from hot combustion gases passing around chamber 4. Air is blown into hollow shaft out through perforated pip 75, and thence up through the body of molten pitch in still 6. Rotation of agitator 5 insures intimate contact between the molten pitch and air rising therethrough, and further maintains more uniform temperature conditions throughout the body of molten pitch. During the reaction the temperature of the still con-tents is maintained between 550 and 950 F. and maybe regulated in a manner well known in the art by controlling the amount and temperature of hot combustion gases passing around still 4. Although temperatures below 550 F. may be employed, the reaction at this lower temperature is unduly long. At temperatures above 950 F. distillation losses are increased and, in addition, operation at these higher temperatures presents a fire hazard. A preferred temperature range of 650 to 850 F. was found convenient and satisfactory in practical operation. The rate of air introduction into the molten hydrocarbon material in blow still d influences the time required to consummate the reaction. At a low rate the reaction tim would be impractically long, and at too high a rate of air introduction it would be difficult to control the temperature of the. molten pitch. In commercial practice air introduced in contact with the molten pitch at the rate of 20 to 50 cubic feet per minute per ton of pitch will in general be found to give good results.

Air is continuously blown down through hollow shaft 5 and out through the perforations in pipe I into the molten pitch maintained at a temperature between 550 and 950 F. until the benzol-insoluble content of the pitch in blow still 4 exceeds 55%. The benzol-insoluble content of the molten pitch in still t may readily be determined by analyzing small samples withdrawn from the body of pitch. As a practical matter, once an operator has acquired experience with a particular pitch and the temperature, tim and air rate conditions necessary to convert the pitch to a material having a benzol-insoluble content in excess of 55%, it becomes unnecessary for him to analyze samples during the operation and he need only duplicate the conditions to which similar pitch had previously been subjected. Ordinarily, it will be found that the benzol-insoluble content of the pitch increases to approximately 65% at the end of five hours, 75% at the end of 6 hours and at the end of 7 hours. It is inadvisable to continue the air blowing to produce a product having a ben-"ol-insoluble content in excess of because the pitch becomes plastic and dough-like and most diiilcult to maintain in an agitated condition. At the start of the operation the molten pitch is in a rather fluid state, and during the course of the reaction the pitch becomes increasingly viscous and of higher melting point, in the nature of a fused mass. On cooling the fused mass is generally dense and vitreous and usually brittle and coke-like in appearance. The yield of air blown pitch resulting from the reaction in blow still 3 is quite high, usually in excess of 70% and more generally 80-85% by weight of the charge of pitch under going treatment in still l from which it will be apparent that a relatively small proportion of undesirable by-products i produced.

As a result of passing air through the body of molten pitch in still a and heating of the pitch there is evolved from the body of pitch residual gases such as nitrogen, unreacted oxygen, carbon monoxide, carbon dioxide together with low boiling hydrocarbon vapors carried by the residual gases. The gases and vapors are released from the top of blow still 4 through opening 8 and directed throughconduit [3 into a conventional condenser not shown in the drawing wherein the gases are cooled by indirect heat exchange with a cooling medium such as water and the vapors are condensed to form a liquid condensate which is collected and may be burned as fuel or disposed of otherwise.

After completion of the reaction, the air-blown pitch is cooled and solidified by discharging the still contents while in a heated fluid condition from the bottom of blow still 5 through line [4 into pitch-bay m which latter is simply a shallow open tank. Cooling and solidification of the pitch may: also be. accomplished:- by the use; off'a conventional flaking drum not shown. in the drawing.

The solidified pitch is directed: through cone veyor 20; to a suitable pulverizerlwherein. the. pitch is ground so that substantially: all the. finely pulverized pitch passes a 200.: sieve. Agaseous propelling means is. frequently used many. of the commercial. pulverizing devices, designated: by numeral i5, with the result that separation. of the gaseous propellent from finely dividedsolids must be eiiected. This may be accomplished-by passing the gaseous propellent carrying the pulverized pitch through conduit: It into. dust. collector I? which may bev of the conventional cyclone type, The gaseous propellentiis released. from the top of dust collector ll through-opening l8 and the pulverized pitch. permitted: to settle in the bottom of'collector IT.

The pitch dust from dust. collector I1 is briquetted in conventional compressing machines designated as briquette press 2| at pressures ranging from 5,000 to 50,000 p. s. i. depending upon the physical structure and density desired in the ultimate product. The briquettes arethen round in a conventional granulator 22 to about a to 25 mesh grain after which the ground briquettes are sized in the usual manner in screen 23. The sized material from screen 23' is then conveyed to calciner 24, desirably a rotary externally heated retort, wherein charring is effected by passing the stream of air or other oxygen-containing gas through the retort in contact with the granular material at. gradually increas ing temperature from below 400 F., preferably from 300 F. to within the range of 400-750 F. Calcination of the granular material is carried out under the conditions of heating just described until there is obtained an infusible char without permitting fusion of the granules or leaving incompletely reacted and fusible residues. Ordinarily eiiective calcination of the granular material will be accomplished in 2 to 8 hours.

The charred material may be finally activated by subjecting it in activator-25 to the actionof steam or flue gases by known procedures while maintaining temperatures of the general order of 1450-2200" F.

From the foregoing the advantages of the present process will be apparent in that heavy oil previously suitable only as a low value fuel prodnot is converted into valuable activated carbon, fuel pitch is converted into higher yields of activated carbon, production of undesirable byproducts is minimized, and the use of solvents for extracting the benZol-soluble material from pitches is eliminated.

In order to clearly show the difierentiation between air blowing of pitch in accordance with the present invention and normal pyrolysis of pitch as is conventional in. the art, a coke obtained by simple pyrolysis of coal tar pitch in a retort, in the absence of air, was compared with the product of air blowing as a raw material for activated carbon production. Both materials were, pulverized, briquetted, granulated, screened and calcined according to the same procedure except that in the briquetting step the pyrolytic coke required addition of about tar as a binder, and even then the pellets were very weak, whereas the briquetting of the air-blown pitch was effected without binder and gave strong, hard pellets. Following calcination, the airblcwn pitch and pyrolytic coke pellets were steam-activated atv 1790 F; and these products were then: evaluated. by the; standard: iodine: ad-'- sorption procedure.-. The activated pyrolytic. coke and air-blown pitch had iodine values of 29.6 and; 79.9., respectively. The high activity fromthe. product of: air-blown pitch clearly differentiates. the. air-blown pitch from the coke'as; a starting material for. activated carbon manu,- facture;

The. following examples illustrate the presentinvention.

Example 1 A" coke-oven tar obtained from the pyrolyti'c decomposition of bituminous coal was subjected todistillation until all the hydrocarbon material boiling bel'ow 680? F. was evolved as vapors, con stituting 55% by volume of the coke oven tar, leaving as. residue a soft plastic pitch. having a melting point of 180 F. The 180 F. pitch was placed in an externally heated vertical vessel'and. heat applied to the walls of the vessel until the pitch became molten and its temperature raised to 710 F. Air was blown through the constantly agitated, body of molten pitch maintained at 700-710 F: at a rate of 32 cubic feet per minute per. ton of pitch for seven hours at the endv of. which time a yield of blown pitch analyzing. 82% benzol-insoluble was obtained. The airblown pitch was then pulverized to pass a. 200. mesh sieve, the powdered pitch briquetted at 5,000 p. s. i., and the briquettes granulated to 10-20 mesh grain. The granulated briquettes were charged to a rotary retort and air passed therethrough while the temperature was gradually increased (over about 5 hours) from 400 E. to 750 F. The resultant char was unfused and infusible, wholly insoluble in benzol. Activation of this granular char at 2010" F. with steam gives an activated carbon whose activity is such that 0.5 gram removed 85% of the color from. ml. of a standard brown sugar solution.

Example 2 A pitch-M 200" F. melting point, obtained by distillationof a crude heavy water-gas tar, was blown with air at 752 F. and an air rate of 35 cu. ft.'/ton/min; for 6 hours. A yield of 78% ofa pitch analyzing 72.8% benzol-insoluble was obtained'. This pitch was pulverized to pass the 200 sieve, briquetted at 5,000 p. s. i. and the briquettes granulated and screened to obtain a 10-20 mesh fraction. The granulated, briquetted pitch was charged to a rotary retort and gradually heated, over a period of about 5 hours, from 400 to 750'F; The resultant char was infusible, and activated readily when reacted with steam at.1800 F. The activity of the product'was such that: 025 gram removed 77% of the iodine from a. standard test solution containing 270 mg. of iodine per hundred m1.

Example 3 amples and was then activated with steam at 1790" F. The activated product had an iodine value of 87 Example 4 A coke-oven tar pitch having a benzol-insoluble content of 31.9% was blown with air ata rate of 32 cubic feet per ton per minute for 3 hours to a benzol-insoluble content of 80%. It was pulverized to such fineness that 80% passed a No. 200 sieve, briquetted at 5,000 p. s. i., and granulated to 10-25 mesh. The granulated briquettes were calcined in air at gradually increasing temperatures of 400-750 F. in about 5 hours. The resultant char was activated with steam at 1800 F. and had an iodine value of 81.5% and adsorbed 53% of its own weight of carbon tetrachloride when in equilibrium with an air stream containing 40,000 p. p m. of that vapor at'77 F.

Although certain preferred embodiments of the invention have been disclosed for purpose of illustration it will be evident that various changes and modifications may be made therein without departing from the scope and spirit of the invention.

I claim:

1. A process for the production of activatable char from high boiling hydrocarbon material derived from Dyrolytic decomposition products selected from the group consisting of coal tar, water-gas tar and oil-gas tar which comprises subjecting said pyrolytic decomposition products to distillation to remove therefrom substantially all the oils boiling below 670 F., passing air in intimate contact with the residual hydrocarbon material maintained at a temperature between 650 and 850 F. at a rate of 20 to 50 cubic feet per minute per ton of residual hydrocarbon material for a sufiicient length of time to convert said residual hydrocarbon material into a product having a benzol-insoluble content of 65 to 85% by weight, pulverizing the air-blown hydrocarbon material to below about 200 mesh size, compressing the pulverized hydrocarbons at pressures ranging from 5000 to 50,000 p. s. i. to form briquettes, crushing and sizing the briquettes into granules of about 4 to 20 mesh size, calcining the granules in the presence of oxygencontaining gas at increasing temperatures from below about 400 F. to not in excess of 850 F. While maintaining the temperatures sufficiently low during such calcination so that the granules remain in an unfused condition, continuing the calcination until an infusible activatable char is obtained, and activating the char at a temperature from 1450 to 2200 F.

2. A process for the production of activatable char from coal tar which comprises subjecting said coal tar to distillation to remove therefrom substantially all the oils boiling below 670 F., passing air in intimate contact with the residual coal tar pitch maintained at a temperature between650and850 F. at a rate of 20-50 cubic feet per minute per ton of residual coal tar pitch for a suflicient length of time to convert said coal tar pitch into a product having a benzol-insoluble content of 65-85% by weight, pulverizing the air-blown pitch to below about 200 mesh, compressing the pulverized pitch at pressures ranging from 5000 to 50,000 p. s. i. to form briquettes, crushing and sizing the briquettes into granules of about 4 to 20 mesh size, calcining the granules in the presence of oxygen-containing gas at increasing temperatures from below about 400 F. to not in excess of 850 F. while maintaining the temperatures suificiently low during such calcination so that the granules remain in an unfused condition, containing the calcination until an infusible activatable char is obtained and 8v activating the char at a temperature from 1450 to 2200 F.

3. A process for the production of activatable char from water-gas tar which comprises subjecting said water-gas tar to distillation to remove therefrom substantially all the oils boiling below 670 F., passing air in intimate contact with the residual water-gas tar pitch maintained at a temperature between 650 and 850 F. at a rate of 20-50 cubic feet per minute per ton of residual water-gas tar pitch for a sufficient length of time to convert said water-gas tar pitch into a product having a benzol-insoluble content of 6585% by weight, pulverizing the air-blown pitch to below about 200 mesh, compressing the pulverized pitch at pressures ranging from 5000 to 50,000 p. s. i. to form briquettes, crushing and sizing the briquettes into granules of about 4 to 20 mesh size, calcining the granules in the presence of oxygen-containing gas at increasing temperatures from below about 400 F. to not in excess of 850 F. while maintaining the temperatures sufficiently low during such calcination so that the granules remain in an unfused condition, continuing the calcination until an infusible activatable char is obtained and activating the char at a temperature from 1450 to 2200 F.

4. A process for the production of activatable char from oil-gas tar which comprises subjecting said oil-gas tar to distillation to remove therefrom substantially all the oils boiling below 670 F., passing air in intimate contact with the residual oil-gas tar pitch maintained at a temperature between 650 and 850 F. at a rate of 20-50 cubic feet per minute per ton of residual oil-gas tar pitch for a sufficient length of time to convert said oil-gas tar pitch into a product having a benzol-insoluble content of 65-85% by weight, pulverizing the air-blown pitch to below about 200 mesh, compressing the pulverized pitch at pressures ranging from 5000 to 50,000 p. s. i. to form briquettes, crushing and sizing the briquettes into granules of about 4 to 20 mesh size, calcining the granules in the presence of oxygencontaining gas at increasing temperatures from below about 400 F. to not in excess of 850 F. while maintaining the temperatures sufiiciently low during such calcination so that the granules remain in an unfused condition, continuing the calcination until an infusible activatable char is obtained and activating the char at a temperature from 1450 to 2200 F.

5. A process for the production of activatable char from high boiling hydrocarbon material derived from pyrolytic decomposition products selected from the group consisting of coal tar, water-gas tar and oil-gas tar which comprises subjecting said pyrolytic decomposition products to distillation to remove therefrom substantially all the oils boiling below 670 F., passing air in intimate contact with the residual hydrocarbon material maintained at a temperature between 650 and 850 F. at a rate of 20 to 50 cubic feet per minute per ton of residual hydrocarbon material for a sufiicient length of time to convert said residual hydrocarbon material into a product having a benzol-insoluble content of 65 to by Weight, pulverizing the air-blown hydrocarbon material to below about 200 mesh size, calcining the pulverized hydrocarbon material in the presence of oxygen-containing gas at increasing temperatures from below about 400 F. to not in excess of 850 F. while maintaining the temperatures suiiiciently low during such calcinationso. that the. hydrocarbon material remains in an unfused condition, continuing the calcination until an infusible activatable char is obtained, and activating the char at a temperature from 1450 to 2200 F.

6. A process for the production of activatable char from coal tar which comprises subjecting said coal tar to distillation to remove therefrom substantially all the oils boiling below 670 F., passing air in intimate contact with the residual coal tar pitch maintained at a temperature between 650 and 850 F. at a rate of 20-50 cubic feet per minute per ton of residual coal tar pitch for a suflicient length of time to convert said coal tar pitch into a product having a benzolinsoluble content of 55-85% by Weight, pulverizing the air-blown pitch to below about 200 mesh, calcining the pulverized hydrocarbon material in the presence of oxygen-containing gas at increasing temperatures from below about 400 F. to not in excess of 850 F. while maintaining the temperatures sufiiciently low during such calcination so that the hydrocarbon material re-' mains in an unfused condtion, continuing the calcination until an infusible activatable char is obtained and activating the char at a temperature from 1450 to 2200 F.

7. A process for the production of activatable char from water-gas tar which comprises subjecting said Water-gas tar to distillation to remove therefrom substantially all the oils boiling below 670 F., passing air in intimate contact with the residual water-gas tar pitch maintained at a temperature between 650 and 850 F. at a rate of 20-50 cubic feet per minute per ton of residual water-gas tar pitch for a suflicient length of time to convert said water-gas tar pitch into a product having a benzol-insoluble content of 65-85% by weight, pulverizing the air-blown pitch to below about 200 mesh, calcining the pulverized hydrocarbon material in the presence of oxygen-containing gas at increasing temperatures from below about 400 F. to not in excess of 850 F. while maintaining the temperatures sufficiently low during such calcination so that the hydrocarbon material remains in an unfused condition, continuing the calcination until an infusible activatable char is obtained and activating the char at a temperature from l450 to 2200 F.

8. A process for the production of activatable char from oil-gas tar which comprises subjecting said oil-gas tar to distillation to remove therefrom substantially all the oils boiling below 670 F., passing air in intimate contact with the residual oil-gas tar pitch maintained at a temperature between 650 and 850 F. at a rate of 20-50 cubic feet per minute per ton of residual oil-gas tar pitch for a sufiicient length of time to convert said oil-gas tar pitch into a product having a benzol-insoluble content of -85% by weight, pulverizing the air-blown pitch to below about 200 mesh, calcining the pulverized. hydrocarbon material in the presence of oxygencontaining gas at increasing temperatures from below about 400 F. to not in excess of 850 F. while maintaining the temperatures sufliciently low during such calcination so that the hydrocarbon material remains in an unfused condition, continuing the calcination until an infusi ble activatable char is obtained and activating the char at a temperature from 1450 to 2200 F.

JOSEPH W. DONEGAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,008,146 Morrell July 16, 1935 2,549,298 Donegan Apr. 17, 1951 

5. A PROCESS FOR THE PRODUCTION OF ACTIVATABLE CHAR FROM HIGH BOILING HYDROCAROBON MATERIAL DERIVED FROM PYROLYTIC DECOMPOSITION PRODUCTS SELECTED FROM THE GROUP CONSISTING OF COAL TAR, WATER-GAS TAR AND OIL-GAS TAR WHICH COMPRISES SUBJECTING AND PYROLYTIC DECOMPOSITION PRODCUTS TO DISTILLATION TO REMOVE THEREFROM SUBSTANTIALLY ALL THE OILS BOILNG BELOW 670* F., PASSING AIR IN INTIMATE CONTACT WITH THE RESIDUAL HYDROCARBON MATERIAL MAINTAINEED AT A TEMPERATURE BETWEEN 650 AND 850* F. AT A RATE OF 20 TO 50 CUBIC FEET 